Busemann’s Biplane

Of some of the various new aircraft concepts to come through the pipeline in the realm of supersonic endeavour, the MIT ‘Busemann’s biplane’, or ‘MISORA’ has to be one of the more ridiculous, but well-intentioned concepts that has come to light.

This design was the subject of an MIT research project and found its way into the heady verse of Popular Science magazine, among other publications, here;

The concept art accompanying the supersonic biplane concept can be seen below;

The images of the Busemann’s biplane concept portray a large, bulbous, high aspect ratio stacked flying wing, with two central stacked powerplants and two more either side.

The PR blurb makes various claims about halving the drag of ‘the’ Concorde with the principle of the stacked supersonic wing, and on this basis the Popular Science journalists took the bait hook line and sinker, and lo and behold, the MISORA concept lives.

Looking at the MISORA concept, my cynical brain immediately kicks into nitpicking mode, and starts shouting out it’s various critical observations and reasons why this design is completely ludicrous, like the massive frontal surface area, the huge wing span and huge pressure wave this would push, the massive engine-out yaw it would suffer if one of those outboard engines failed, the short pitch-moment arm that would likely prevent it from even taking off, the abominable area-ruling, the shear absence of any kind of sears-haack blending, the annoyingly childish go-faster streaks. I HATE this plane…and I hate even more that in its utter ridiculousness, PopSci journalists actually entertain this as a valid aircraft concept while my own design languishes in obscurity. (Sob, sob)

But, I’m whining… get over yourself Pete. Think about it – could this actually work? And if any aspect of it could work, how could that technology benefit a more sensible-conventional SST concept?

So let’s study it – what was Adolph Busemann actually thinking when he coined his ‘biplane’? He was not imagining a bulbous supersonic biplane per se, but simply the diffusion of a supersonic shockwave in a sharp-edged venturi, as illustrated below.

To stretch the imagination to the assumption that these opposing flat plates could actually be lifting wings, is perhaps missing one of the more exciting prospects for this technology. The MISORA concept only presumes that this would be deployed for an aircraft-scale application, and eliminate the boom completely by flying perfectly perpendicular to the air stream, and that the aerodynamics of said aircraft would be purely two dimensional…

The applications I see for a busemann’s biplane are not whole-aircraft scaled; I see the cross section of a supersonic turbojet inlet, or even an air conditioning inlet, maybe even a ramjet providing extra thrust during supercruise, as shown in the image below, a supersonic venturi is an excellent ‘air digester’, creating a self-cancelling sonic shockwave, resulting in a diffused and decompressed gas stream on the outlet of the choke point – but I just can’t see the aircraft level application working.

BUT – I did decide to TRY to believe in this, I used the existing concept images to attempt a slightly less Isaac Asimov version of MISORA, adjusted for more realistic scale and proportion…

The results of my impression of the MISORA are shown below, beside Concorde and Tu-144 for comparison. Using some bits of the Northrop B2, and Tu-144 tailfins, I’ve tried to respect the general layout that the original etsy artist ‘designer’ came up with, however mine is a bit flatter, and the tailfins are moved out to compensate for the yaw of those engines.

Looking at this sketch, certainly beside genuine supersonic brethren, the sonic wave drag problems with MISORA are vividly obvious, the size of the Mach cone would be more like a Mach ice-cream sandwich, it would not be able to get ‘over the hump’; consequently it simply won’t work and is not worth entertaining as an aircraft configuration, but the potential applications elsewhere on a more conventional aircraft are manyfold, air intakes and engine inlets and so on.

But, it was fun to imagine for a little while – Asimov would have loved it on the cover of one of his books.